Study On The Structural Phase Transition And Properties Of Nitrate Complexes

Structural phase transition is a phase transition in which the crystal structure of a material changes under external stimuli such as temperature and pressure,resulting in a broken symmetry.It is the basic feature of phase change.Want to obtain phase change materials with good performance,the resulting crystal needs to induce structural phase change.This paper describes in detail a series of compounds synthesized by monovalent anion nitrate as bridging ligand,and study the crystals of these compounds for structural phase transition studies,various characterizations are used to analyze the properties of these compounds(X-ray Single Crystal Diffractometer,Differential Scanning Calorimeter,etc.).The realization of these nitrate complexes in terms of ferroelectricity,tunable photoluminescence will make people very interested in the study of its structure and thermodynamics.It also injects new vitality into the content of ferroelectric materials and discovers new potential applications.The research content of this paper is as follows:(1)All crystals are not ideal,and many of their properties are often determined not by the regular arrangement of atoms,but by the irregular arrangement of crystal defects.Many properties of materials can be controlled effectively by proper use of solid defects.Here,we describe metal-vacancy-induced ferroelectricity in pseudo coordination polymers,(H₂dabco)₂M(H₂O)₂(NO₃)₆(dabco=1,4-diazabicyclo[2.2.2]octane,M=Cd²⁺or Cu²⁺).By doping divalent M ions into a hexagonal perovskite structure(H₂dabco)(NH₄)(NO₃)₃,we obtained M-vacancy(V_M)compounds(H₂dabco)₂(M(H₂O)₂)_x(NH₄)_2-2x(NO₃)₆(0?x?1).The coordination twist of V_M leads to instability of the lattices,structural phase transitions and striking ferroelectricity and related properties.By adjusting the content of the M ions/vacancy,we can tune the symmetry and ferroelectricity of the crystals,which reveals that the vacancy can be utilized as an element to produce ferroelectricity.This finding should stimulate further synthesis for novel properties,and may start the chemistry of metal-vacancy coordination compounds.(2)Perovskite in the ideal ferroelectric material has been extended to hybrid materials,but is mainly limited to alkali metals/NH₄⁺halides and metal formates.In order to obtain new functions or better performance hybrid perovskite ferroelectrics.I successfully synthesized a new family of MX₃ hybrid perovskites using monovalent nitrate as a bridging ligand,four compounds were successfully synthesized.The results show that nitrate perovskite provides a promising platform for realizing new properties.The structural diversity and adjustable ferroelectric properties make it suitable for a wide range of potential applications,and more hybrid perovskites can be prepared by using nitrate as the anion at the X position.(3)Synthesis of a new hybrid luminescent material compound:(3HQ)₄[Rb Eu(NO₃)₈](3HQ=3-quinuclidinone),it undergoes a reversible phase change and a reversible phase transition at T_c=438K.At the same time,it was also identified and found that the compound has photoluminescence properties under ultraviolet excitation.Exposing a colorless sample to ultraviolet light can emit bright orange-red light.Hybrid rare-earth double perovskites are expected to play a role in the preparation of multifunctional light-responsive and electrical-responsive devices,and ultimately benefit the application of stimulus-responsive materials.